/*
 * Copyright 2014 The Netty Project
 *
 * The Netty Project licenses this file to you under the Apache License, version 2.0 (the
 * "License"); you may not use this file except in compliance with the License. You may obtain a
 * copy of the License at:
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */
package io.netty.handler.codec.http2;

import io.netty.channel.ChannelHandlerContext;
import io.netty.util.internal.UnstableApi;

/**
 * Base interface for all HTTP/2 flow controllers.
 */
@UnstableApi
public interface Http2FlowController
{
    /**
     * Set the {@link ChannelHandlerContext} for which to apply flow control on.
     * <p>
     * This <strong>must</strong> be called to properly initialize the
     * {@link Http2FlowController}. Not calling this is considered a programming
     * error.
     * @param ctx The {@link ChannelHandlerContext} for which to apply flow
     *        control on.
     * @throws Http2Exception if any protocol-related error occurred.
     */
    void channelHandlerContext(ChannelHandlerContext ctx) throws Http2Exception;

    /**
     * Sets the connection-wide initial flow control window and updates all
     * stream windows (but not the connection stream window) by the delta.
     * <p>
     * Represents the value for <a href=
     * "https://tools.ietf.org/html/rfc7540#section-6.5.2">SETTINGS_INITIAL_WINDOW_SIZE</a>.
     * This method should only be called by Netty (not users) as a result of a
     * receiving a {@code SETTINGS} frame.
     *
     * @param newWindowSize the new initial window size.
     * @throws Http2Exception thrown if any protocol-related error occurred.
     */
    void initialWindowSize(int newWindowSize) throws Http2Exception;

    /**
     * Gets the connection-wide initial flow control window size that is used as
     * the basis for new stream flow control windows.
     * <p>
     * Represents the value for <a href=
     * "https://tools.ietf.org/html/rfc7540#section-6.5.2">SETTINGS_INITIAL_WINDOW_SIZE</a>.
     * The initial value returned by this method must be
     * {@link Http2CodecUtil#DEFAULT_WINDOW_SIZE}.
     */
    int initialWindowSize();

    /**
     * Get the portion of the flow control window for the given stream that is
     * currently available for sending/receiving frames which are subject to
     * flow control. This quantity is measured in number of bytes.
     */
    int windowSize(Http2Stream stream);

    /**
     * Increments the size of the stream's flow control window by the given
     * delta.
     * <p>
     * In the case of a {@link Http2RemoteFlowController} this is called upon
     * receipt of a {@code WINDOW_UPDATE} frame from the remote endpoint to
     * mirror the changes to the window size.
     * <p>
     * For a {@link Http2LocalFlowController} this can be called to request the
     * expansion of the window size published by this endpoint. It is up to the
     * implementation, however, as to when a {@code WINDOW_UPDATE} is actually
     * sent.
     *
     * @param stream The subject stream. Use
     *        {@link Http2Connection#connectionStream()} for requesting the size
     *        of the connection window.
     * @param delta the change in size of the flow control window.
     * @throws Http2Exception thrown if a protocol-related error occurred.
     */
    void incrementWindowSize(Http2Stream stream, int delta)
            throws Http2Exception;
}
